Classification of Mutations

Question 1

Different ways mutations can be classified

Question 2

Classification by Origin - Spontaneous

Answer 2

• Occurs without a mutagen - no external factors
• Usually due to errors in DNA replication or effect of endogenous compounds present in cell e.g. reactive oxygen species damaging DNA

Question 3

Classification by Origin - Induced

Answer 3

• Caused by mutagen
  e.g. chemical or physical agent increase rate of mutagenesis
• Can cause increase rate of spontaneous mutation or damages DNA itself

Question 4

Classification by cell type - Somatic

Answer 4

In non-reproductive cells
- not passed to next generations
- can lead to diseases e.g. cancers + are responsible for aging

Question 5

Classification by cell type - Germ-line

Answer 5

Occurs in reproductive cells
- Mutation will be passed to next generations
- Responsible for genetic variation

Question 6

Classification by expression - Unconditional

Answer 6

• Mutation is expressed at all times

Question 7

Classification by expression - Conditional

Answer 7

• Expressed under certain conditions
• E.g. temperature sensitive will only have a phenotypic effect at certain temps due its effect on proteins

Question 8

Classification by effect on function: Loss-of-function

Answer 8

Also known as a knockout or null mutation
- Eliminated normal function

Question 9

Classification by effect on function: Hypomorphic

Answer 9

Also called ‘leaky’
- Reduces normal function

Question 10

Classification by effect on function: Hypermorphic

Answer 10

• Increases normal function

Question 11

Classification by effect on function: Gain-of-function

Answer 11

Also known as ectopic expression
- Expressed at the incorrect time or in inappropriate cell types

Question 12

Mutations’ effect on function

Answer 12

• may be positioned in ‘junk’ DNA (likely no effect), control sequences (control transcription) and protein-coding region
• May be in promoters (could knock it out causing loss of function or increase protein production)

Question 12

Classification by molecular change - Base substitution

Answer 12

One bp replaced with a different one
-Transition which are more common (pyrimidine -> pyrimidine or purine -> purine) so A-T becomes G-C

• Transversion - (pyrimidine -> purine or vice versa) A-T becomes T-A for example

Question 13

Classification by molecular change - Insertion

Answer 13

1 or more extra nucleotides present

Question 14

Classification by molecular change: Deletion

Answer 14

1 or more missing nucleotide